This invention relates to a process for manufacturing a metallized polymeric film as well as the film resulting from the process. More particularly, the invention provides a metallized, e.g., aluminized, polymeric film wherein the metal-adherent surface is a flame treated crystalline polyolefin such as isotactic polypropylene containing from 0 to about 50 weight percent of non-crystalline polyolefin component(s).
The metallization of polymeric films for aesthetic and/or functional purposes is a well developed technology.
U.S Pat. No. 3,431,135 describes the vacuum metallizing of polyethylene terephthalate film in which the film is first subjected to a reducing flame to improve its affinity for the subsequently applied metal. This procedure is said to result in a level of bond strength between the film and metal which is higher than that resulting from treatment of the film surface by neutral and oxidizing flame treatment or electrical discharge treatment.
U.S. Pat. No. 3,674,536 describes a method for metallizing a crystalline polyolefin film surface employing established vacuum metallizing techniques. Adhesion of the metal to the film substrate is said to be improved by incorporating a coumarone-indene resin into the metal-adherent resin.
U.S. Pat. No. 4,211,811 describes the vacuum metallizing of an oriented, i.e., stretched, crystalline polyolefin film whose surface has been treated by corona discharge to improve its receptivity for the subsequently applied metal film. Similar procedures are described in U.S. Pat. Nos. 4,345,005 and 4,604,322, the metal-adherent film surface being fabricated from an ethylene-propylene copolymer.
U.S. Pat. No. 4,357,383 described a multiple-layer metallized film comprising a polyolefin copolymer substrate layer and a metal-adherent random ethylene copolymer layer for improved metal adhesion.
U.S. Pat. No. 4,508,786 describes a corona discharge-treated vacuum metallized resin film wherein the resin is obtained by blending a crystalline propylene-alpha-olefin copolymer containing 70% by weight or more of propylene component and having a crystalline m.p. of 150.degree. C. or lower, with a high density polyethylene having a density of 0.940 g/cm.sup.3 or higher, in blending ratios of 96 to 80% by weight of the copolymer and 4 to 20% by weight of the polyethylene, the ratio of the melt flow rate of the polyethylene to that of the copolymer being equal to or greater than 0.7.
U.S. Pat. No. 4,522,887 describes a laminate film prepared by laminating at least one surface of a biaxially oriented polypropylene film (A) with an olefin polymer film (B) containing from 10 to 50% by weight of an ethylene component with the balance mainly comprising a propylene component. Olefin polymer film (B) possesses at least three peaks in the melting curve within the range of from 120.degree. to 165.degree. C. and a surface roughness Ra of from 0.2 to 1.5 microns. The film is said to possess excellent adhesion to metallized layers and to paper. In addition to various vacuum metallizing techniques, other metallization procedures are disclosed as suitable, i.e, sputtering and ion plating. The preferred metallization procedure includes activation of the film surface to which the metal is to be applied by a treatment such as corona discharge, acid or flame.
Treatment of a polymer film surface by flame to improve the adherence of a subsequently applied coating is a well known type of operation in the coated polymer film art. Illustrative flame treatment techniques are described, inter alia, in U.S. Pat. Nos. 2,632,921; 2,648,097; 3,028,622; 3,255,034; 3,347,697; 3,375,126; and 4,239,827.
Heretofore, it has not been recognized that a crystalline polyolefin film surface can be flame treated prior to vacuum metallization to provide a level of film-metal adherence which is significantly greater than that achieved by corona discharge treatment of such a surface prior to metallization or by flame treatment of an essentially non-crystalline polyolefin homopolymer/copolymer surface.